In a conventional in-wheel motor driving system, a motor is disposed in an outer frame, and an output shaft of the motor is rotatably supported by the outer frame via a bearing. The output shaft has one end coupled to a wheel via a planetary gear.
Further, the outer frame housing the motor is coupled to a suspension arm via a ball joint. The suspension arm is coupled to the vehicle body via a shock absorber.
As such, in the conventional in-wheel motor driving system, the outer frame housing the motor is coupled to the vehicle body via the ball joint and the suspension arm.
As a conventional in-wheel motor driving system, one having a hollow motor supported by a motor suspension is known from Go Nagaya, Yasumichi Wakao, Akihiko Abe, “Development of an In-Wheel Motor with Advanced Dynamic-Damper Mechanism”, Society of Automotive Engineers of Japan, Inc., Nov. 26, 2002, Preprints of Meeting on Automotive Engineers, No. 83-02, pp. 9-12. The hollow motor is coupled to a wheel, and rotates the wheel. The hollow motor is supported by the motor suspension in a manner capable of vibrating in the up-and-down direction of the vehicle, and is separated from the unsprung mass. The wheel is supported by the suspension arm at the vehicle body. In this in-wheel motor driving system, when the wheel vibrates, the vibration is transmitted from the wheel to the hollow motor, so that the hollow motor comes to vibrate in the up-and-down direction of the vehicle. Such vibration of the hollow motor reduces the vibration of the unsprung components transmitted to the vehicle.
In the in-wheel motor driving system disclosed in the above document, however, the outer frame housing the motor is supported by the suspension, and thus, the wheel may receive unexpectedly large external force depending on the road conditions and the like. When such unexpectedly large external force is input to the wheel, the outer frame may come into contact with other components such as a knuckle and the like. If the outer frame comes into contact with the other components, sound and impact will be transmitted to the vehicle body, leading to degradation in riding comfort of the vehicle.